i have just finished a simple arrangement of this bach masterpiece, played on an acoustic guitar, a flute and GPO cello.
it took me some time to learn the guitar fingering, but it was worthwile! :-)
for the GPO cello i tried the Big Bob SIPS script for legato, and i can say that it is wonderful!
A very interesting interpretation of a great piece.
While listening to it I found that the only thing I did not find convincing about the cello was the legato. I would not mention this because it for not appearing too picky ... but rereading your post I saw that this has been an issue here.
Maybe I don't get something very valuable ... but why don't you use just the common legato technique? I seem not to get the point here.